1. Field of the Invention
The present invention relates to devices for treating semiconductor wafers utilizing a plasma generated by a gas discharge.
2. Description of the Prior Art
In the production of semiconductor devices such as transistors and integrated circuits, semiconductor substrates, or wafers, are subjected to treatments such as thin film formation etching, oxidation, and doping. Some of such wafer treating devices utilize a plasma generated by a gas discharge. Recently, wafer treating devices utilizing a plasma generated by a gas discharge driven by electron cyclotron resonance (ECR) have been developed. These devices have a number of advantages over conventional chemical vapor deposition devices, including low operating temperatures and high treatment quality.
U.S. Pat. Application Ser. No. 357310 teaches a fundamental structure of such semiconductor wafer treating devices utilizing a plasma generated by electron cyclotron resonance. As shown in FIG. 3 of the drawings, such a device generally comprises a wafer treating chamber 1 accommodating a holder 8 holding a wafer 9, and a plasma generating chamber 2 disposed adjacent to and in direct communication with the wafer treating chamber 1. Microwave energy generated by a microwave source (not shown) is introduced into the plasma generating chamber 2 through a waveguide 3 and a quartz plate 4. Further, a solenoidal electromagnetic coil 5a surrounds the plasma generating chamber 2 to generate a magnetic field in the plasma generating chamber 2 and the wafer treating chamber 1. A gas introducing port 6 and a gas exhausting port 7 are formed in a wall of the plasma generating chamber 2 and in a wall of the wafer treating chamber 1, respectively.
The operation of the device of FIG. 3 is as follows. After the gas remaining in the chambers 1 and 2 is thoroughly exhausted from the port 7, a reactive gas is introduced into the chambers 1 and 2 through the port 6; at the same time, a part of the gas is exhausted from the port 7 to keep the pressure thereof at a predetermined level. Next, a microwave energy having a frequency of 2.45 GHz generated by the microwave source (not shown) is supplied to the plasma generating chamber 2 through the waveguide 3 and the quartz plate 4. Simultaneously, the coil 5a is energized to produce a magnetic field in the plasma generating chamber 2 and the wafer treating chamber 1; the flux density of the magnetic field in the plasma generating chamber 2 is regulated to 875 G to produce electron cyclotron resonance therein in cooperation with the microwaves; the magnetic field produced by the coil 5a in the wafer treating chamber 1 diverges from the plasma generating chamber 2 to the holder 8.
Thus, the electrons in the plasma generating chamber 2 are accelerated in helical paths in electron cyclotron resonance in the chamber 2, absorbing the energy from the microwave; the collisions of these fast moving electrons generate a dense gas plasma in the plasma generating chamber 2. The plasma thus generated is transported to the wafer 9 along the diverging lines of the magnetic field produced by the solenoidal coil 5a. Thus, the treatment of the wafer 9, e.g. thin film formation or etching, is effected on the surface thereof. As is well known, the kind of the gas utilized in the treatment or the pressure thereof, the power of the microwave source, etc., are chosen according to the type of the treatment which is effected on the wafer.
The conventional ECR plasma wafer treating devices, however, have disadvantages as described below.
Since the conventional ECR plasma wafer treating devices utilize a solenoidal coil to produce a magnetic field therein, the magnetic field thus produced in the plasma generating chamber 2 is the strongest along the central axis thereof. Electrons in the plasma generating chamber 2 are thereby forced to move radially from the central axis toward the outer peripheral portions thereof. As a result, the confinement of the electrons therein is insufficient, and the density of plasma generation therein cannot be made as high as desired. Consequently, the speed of the reaction of the wafer treatment is low. Further, due to the insufficient confinement of the electrons, the plasma generated in the plasma generating chamber 2 is unstable so that the wafer treating process suffers a number of restrictions such as on the kind of the gas utilized in the generation of the plasma or the pressure thereof and the level of the output power of the microwave utilized to produce electron cyclotron resonance.